Satellites reveal differences in sea level rises

November 24, 2010
By Phillip F. Schewe

Glaciers are retreating and parts of the ice sheets on Greenland and Antarctica are melting into the ocean. This must result in a rise in sea level, but by how much? A new measurement of the gravity everywhere around the globe with a pair of orbiting satellites provides the first ever map detailing the rises across different parts of the globe.

According to the new results, the annual world average sea level rise is about 1 millimeter, or about 0.04 of an inch. In some areas, such as the Pacific Ocean near the equator and the waters offshore from India and north of the Amazon River, the rise is larger. In some areas, such as the east coast of the United States, the sea level has actually dropped a bit over the past decade.

The surface of the sea is a constantly shifting fabric. To achieve a truer sense of how much the sea is changing in any one place, scientists measure the strength of gravity in that place. Measuring gravity over a patch of ocean or dry land provides an estimate of how much mass lies in that region. The measured mass depends on the presence of such things as mountains, glaciers, mineral deposits, and oceans.

If the gravity measurement for a place is changing, this could mean that the place is losing mass because of a retreating glacier or gaining mass if, as in the ocean surrounding Antarctica, new melt water is streaming in.

The Gravity Recovery and Climate Experiment, or GRACE for short, consists of a pair of satellites moving in an orbit that takes them over the South and North Poles. The two craft, nicknamed Tom and Jerry after the television cartoon characters, send constant signals to each other to determine their relative spacing to about 10 microns -- one-tenth the width of a human hair -- over a distance of 130 miles. If the first craft flies above a slightly more weighty area of the Earths' surface -- like a mountain range -- it will be tugged a bit out of place, an effect picked up by a change in the relative spacing of the craft.

In these way monthly gravity maps of pieces of land or ocean about 180 miles wide can be made with high precision. The new report for the years of 2003-09 looks at how much mass has been lost from land areas and how much mass has been gained by ocean areas.

One of the authors of the report, Riccardo Riva from the Delft University of Technology in the Netherlands, said that average annual rise in sea level rise due to meltwater entering the ocean is about 1 millimeter, but that an additional rise will come from that fact that as the average temperature rises so does the ocean temperature, which in turn causes the volume of the ocean to increase.

"The most important result of the new report is the measurement of the sea level changes for specific regions of the Earth that are based on direct and global measurements of mass change," Riva said.

Mark Tamisiea, who works at the National Oceanography Centre in Southampton, England, and was not involved in the GRACE work, believes the new report represents good research.

"As coastal sea level changes impact society, it is important for us to understand as much about the local differences from the global average as possible," Tamisiea said. "These results are one piece in that puzzle."

"GRACE is definitely the 'real deal' when it comes from measuring climate change from space," said Joshua Willis, an ocean expert at the Jet Propulsion Laboratory in Pasadena, Calif. "This work by Dr. Riva and company reminds us that the world's oceans don't behave like a giant bathtub. As the ice melts and the water finds its way back to the ocean, the resulting sea level rise won't be the same all over the world."

"These effects are still small in today's rising ocean, but as we look out over the next century, the patterns of sea level change due to melting ice will be magnified many times over as the ice sheets thin and melt," Willis said.

Looking at the actual map of sea level rises presents an ironic twist. Offshore the areas where melting ice is most rapidly falling into the ocean -- such as Greenland and Antarctica -- the sea level appears to be falling.

"The main reason for this is the rebound of the solid Earth," explained Riva. "Less ice causes the continents go up, and therefore sea level drops. Meltwater distributes around quite quickly, in most cases, so there is no accumulation due to that."

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It does take more than two satellites to measure position, but we're measuring the height of a "plane", not a position.

I think the data is accurate, so it's definitely a candidate for selective data disposal to effectively continue the GW revenue stream.

Otherwise the models used to predict sea level rise on the US east cost, and in the Arctic, would be called into question, which would further validate the entire conspiracy that says that the models on which this multi-$billion industry is built are flawed. That would not be good for the eugenics, er... I mean, over-population agenda, especially given the revelations that the entire population of the world could live comfortably in ANY ONE of a number of U.S. states.

Better yet, we need to find a way to use this to the advantage of the GW cause. How about this one... the melt is causing land masses to inflate which could lead to potentially severe geological events, with unforeseen consequences.

There seem to be quite a few different overlapping effects that account for changes in gravity, besides sea level change. After spending some time over at the JPL site and graphing some of the raw data myself, I see some interesting things.

Graph this data yourself and run a linear trend line, and I see a significantly flatter trend in this data for the oblateness of the earth than they show on their graph of the same data. The sigma graph is also curious in relation to the actual data.

There are no glaciers on the east coast of the US, but there are melting glaciers on the west coast, where sea level seems to be rising. His theory doesn't 'hold water'.

Well.....

There's a few other mitigation factors that the abstract doesn't talk about. You have the massive amounts of fresh water that are dammed up in the northern hemisphere, (to the point where it may actually affect the spin speed of the earth a miniscule amount).

Then you have the thermal expansion of the water, which will naturally be higher on average around the equator which the above map seems to indicate. Then you have changes in thermohaline currents, etc.

It's a complex thing to examine. One piece of info I got, which is very important to a lot of the debate questions involved, is the fact that it appears our former measurements of sea level rise were off by 50% on the high side. That changes a lot of the research out there currently, and drastically affects a lot of precipitation models.

Gswift, you are right considering east/westcoast, but we might have to consider other factors at play as well,

For instance, the atlantic conveyer belt wich transports water from the atlantic round greenland to the beringstrait and the pacific, as it does so, the water cools down and shrinks in volume in northern atlantic/east coast of usa and will start to warm up/expand once passed through the beringstraight supplemented with the extra meltwater from a rising greenland, wich put a lot of extra volume into the pacific and might partially offset the glacial effects on the westcoast.

What you need to understand is that the "data" shown here is actually a model based, in part, on the GRACE data.

In one sense there is nothing wrong with that, you have data on gravity and want to convert it to data on sea level rise, that is what you do. But the article here ignores the difference, while the original journal article doesn't. For example, estimates of sub-sea water temperatures are pretty rough, and they don't seem to have dealt at all with salinity gradients.

Net result, it is a good start at estimating sea levels from GRACE data integrated with other sources, but there is still a lot of work to do.

I am on my way to the door right now to see about buying some beachfront property near the summit of Mt Everest, since all those glaciers will be gone by 2035. I'll build a nice summer home with a boatdock there.

It may have been panned by the critics, but it looks like "Waterworld" got it right.

But I am so disappointed in the President. He promised that the seas would start receding now that He was Risen.

"One piece of info I got, which is very important to a lot of the debate questions involved, is the fact that it appears our former measurements of sea level rise were off by 50% on the high side"

"Net result, it is a good start at estimating sea levels from GRACE data integrated with other sources, but there is still a lot of work to do"

Maybe those two statements explain each other? The previous sea level estimates could still be more accurate than this work, but I really don't think anyone knows for sure right now. Sea level is SO difficult to measure globally. This certainly flies in the face of everything people here have argured with me about here in regard to the clear evidence that sea level here in Charleston South Carolina hasn't risen in recorded history. People here have called me an idiot for saying that, but the evidence is impossible to deny. This study would support the simple observations I can make by walking down to the historical sights and looking around.

Skeptic you are certainly right about the huge implications this would have if it's correct. I don't think this one study is enough to overturn any of the other opinions yet though.

I expect a similar result, in terms of earth-shaking new data, as the STEREO and other new solar observatories begin to return meaningful data sets. There's going to be a few bad days for people who have been over-confident in current climate theory in the not so distant future I think.

It's just common sense. Nobody ever really studied global climate until the past couple of decades. It's a science in its early stages of maturity, and it's a bear in terms of complications and spotty data. We don't even know if we are measuring all the important parts yet, much less figuring out how to accurately measure them once we identify them, and then get a good long data set to derive trends over the noise.

The result will be the ability to go back and check and verify GRACE and improve the data already taken. GOCE will also be able to serve as the benchmark for the use of laser and microwave altitude measurements.

The uncertainties as pointed out by both SH and GS will be quantified and reduced over the next few years. We can expect to much better understand the changes in gravitation and sea level. The questions of the sea temperature profiles are also being worked out by combining the satellite information with actual profile measurements by a number of different means. What we see here is among the first of the articles refining the H2O balance. Great Stuff.

Sea level rise is here estimated at 1.0mm/year, down from 1.8mm/yr for the 1885-1980 average. Hansen says 3.2mm/yr. Disaster is in the m/100 years or >9mm/yr range. This requires 3 - >9 times the fresh water input to occur. Where/when/how is there eveidence of this increasing trend? Nowhere. But does the MSM notice this. We should send them all calculators.

1) measuring ocean "levels" using gravity takes no account of increases due to reductions in density, eg. a) increased water temperature b) reduced water salinity. What these satellites are measuring is very questionablely directly related to ocean level rises.

2) Making conclusions on worldwide climate from observations of ocean levels on a single N. Carolina beach is entirely pointless. Any indicators could be entirely swamped by several factors such as crustal rebound, plate interactions, deep mantle activity, etc. etc.

3) We've only pushed the atmosphere's GHG levels significantly above normal for a very few years, perhaps 3 decades. Expecting any results of that to be definitely measurable yet indicates a poor grasp of reality.

4) Physics tells us that increasing atmospheric GHG loads should cause warming. The difference in average surface temperature of Moon and Earth (Earth about 33 degC warmer) can be fairly much entirely ascribed to the GHG's in earth's atmosphere. In long-term ice core records over past ice ages, atmospheric warming and cooling were quite significantly co-related in time with GHG levels.

At that point, one must start taking an "insurance protection" attitude and start implementing ways to halt the process until enough is known "without a doubt" to make rational decisions.

James Hansen et al claim global sea level rose at 1.7 or 1.8 mm/year during the last century, and that the rate is accelerating. But the best tide station data shows coastal sea levels rose an avg of only ~1.1 mm/year during the last century, and the rate has NOT measurably accelerated in response to increasing atmospheric CO2 emissions.

Actually physics says that there are many factors in global temperature other than ghg's, and the relative roles of each are still poorly understood.

In long-term ice core records over past ice ages, atmospheric warming and cooling were quite significantly co-related in time with GHG levels

The longest and most complete ice core records show a natural trend where warming happens before CO2 increase, and cooling happens despite high CO2 levels. The ice cores are one of the biggest anti-AGW talking points.

At that point, one must start taking an "insurance protection" attitude and start implementing

That's an opinion. I disagree. We have a limited amount of money. Do we spend it on GHG's? Or do we spend it on medicine, education, food, crime, security, water, energy, theoretical sciences, transportation, land conservation, etc? Why spend billions when it may be a waste?

When ice melts, the volume decreases while level stays relatively the same due to density. Personally, it doesn't look to be enough ice on land to make that much difference if it all melted and ended up in the ocean. To say that the oceans would rise by a certain amount, you would have to have several feet of ice covering all the earth's land to raise the oceans.

The variance between models and observation is most likely due to assumptions about thermal expansion of the oceans. I believe the models assume that the whole ocean will warm and expand, but in reality it's starting to look like it's only the surface of the ocean that's warming, so expansion isn't a big factor. Since thermal expansion is assumed in the models to account for about half of the total sea level rise, that would account for the variance nicely. That doesn't mean that's the answer, but it's possible. This study merely points out the already known fact that more research is needed before any predictions can be made. They need to either confirm of deny these results, but it's exceedingly difficult to callibrate this kind of measurement, so it may be years before they have a confident answer. I think this release is premature really.

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